A research program dealing with the biochemistry and pharmacology of endogenous opioid peptides. Particular attention is given to the formation, metabolic inactivation, and binding sites for those materials. The work has five foci: covalent modifications of endogenous peptides; effects of narcotic administration on regulation of peptide synthesis; enkephalinase as an enzyme involved in the inactivation of opioid peptides; multiple opiate receptors in brain; and effects of morphine administration during pregnancy on maternal-fetal peptide systems. In each area, investigations using administration, withdrawal, and addiction to opioids are central. Through such studies we would hope to learn more about basic mechanisms related to morphine use and abuse.